This should be reviewed once we switched to an ESR60-based tor-browser branch.

Is this something we could merge before switching to ESR60, or would this cause some issues with the ESR52 build?

I doubt it would cause issues. I think I just don't want to have this in the next alpha (to avoid surprises) assuming this is the last one ESR52-based. Once it is out next week. I am fine merging this patch even though we might not directly switch to ESR60 then.